A thermodynamic approach for preparing oxide dispersion-strengthened Ti-6Al-4V powder by in situ gas atomization method

This study examined the feasibility of in situ fabrication of oxide dispersion-strengthened (ODS) Ti-6Al-4V (Ti64) powder through a gas atomization (GA) method. Thermodynamic calculations were performed to design the ODS Ti64 by deriving compositions of yttrium oxide (Y2O3), which is completely dissolved into the molten Ti64 and subsequently reprecipitated during cooling in the GA process. In addition, the changes in the equilibrium phase fractions based on varying the Y2O3 content and oxygen (O) concentration in the Ti64 matrix were investigated. From the thermodynamic calculations, an optimal composition for the ODS Ti64 alloy was determined, involving the addition of 1 wt% Y2O3 to Ti64 with an O concentration of 0.1 wt%. The alloy ingot was prepared via vacuum arc remelting, leading to the precipitation of coarse Y2O3 along grain boundaries because of a slow cooling rate. The ODS Ti64 powder was fabricated through an electrode induction melting GA method, and the resulting ODS Ti64 powder had spherical morphology, with uniformly distributed Y2O3 particles of several tens of nanometers in size. The hardness of a conventional Ti64 powder was 354 HV, significantly increasing to 485 HV in the ODS Ti64 powder due to the Y2O3 nanoparticles' dispersion. This study introduces a novel methodology for fabricating high-quality ODS Ti64 powder by the in situ GA method.